A co-founder of file-sharing website Pirate Bay was sentenced to two years in jail for hacking into computers at a company that manages data for Swedish authorities and making illegal online money transfers, a court said.

Gottfrid Svartholm Warg was extradited to Sweden last year from Cambodia to begin a one-year jail sentence after being convicted in 2009 of internet piracy. He was then charged by authorities as part of the separate hacking investigation.

"The hacking has been very extensive and technically advanced," the Nacka district court said in a statement. "The attacker has affected very sensitive systems."

He had denied the charges.

Prosecution documents say Warg, a 28-year-old Swede, managed to transfer 24,200 Danish crowns (NZ$4736) online, but also attempted, in several different transactions, to transfer a total of around €683,000 (NZ$1.15 million).

The investigation was into data infringement involving outsourcing firm Logica.

Swedish authorities have said the hackers gained access to information on several people with protected identities.

In the 2009 trial, a court in Sweden - where The Pirate Bay was founded in 2003 - fined and sentenced to jail Warg and two co-founders then behind the site for breaching copyright in a case brought by firms including Sony Universal Music and EMI.

Swedish prosecutors in May launched a new attempt to close down Pirate Bay, which provides links to music and movie files stored on other users' computers.

The site is now run by an unknown group and uses a domain name registered in Sint Maarten, a Dutch territory in the Caribbean.